1. Field of the Invention
The present invention generally relates to the control of a bidirectional switch by a control circuit, such as a microprocessor, in the case where the control circuit is not referenced to the same reference voltage as the bidirectional switch control terminal.
2. Discussion of the Related Art
As illustrated in FIG. 1, there are many cases in which a control circuit μP supplied between a first voltage V1 and a first reference voltage or first ground G1, is intended to control a bidirectional switch TR referenced to a second reference voltage or ground G2. Bidirectional switch TR is for example intended to switch a load L supplied by the A.C. supply network (currently at 50 or 60 Hz). It is necessary to provide an isolation circuit between the control circuit and the bidirectional switch. A galvanic isolation circuit 1 such as an optocoupler comprising a photoemitter 2 and a photoreceiver 3 is currently used. Photoemitter 2, for example a photodiode in series with a transistor, is connected between supply voltage V1 of the control circuit and ground G1 of the control circuit. Photoreceiver 3, such as a phototransistor, is supplied between a supply voltage V2 derived from the A.C. voltage applied to the load and ground G2. A resistor 4 is arranged in series between voltage V1 and the collector of transistor 2. An impedance 5 is connected between phototransistor 3 and voltage V2. When transistor 3 is controlled to the on state, switch TR is controlled.
Although galvanic isolation circuit 1 is illustrated in FIG. 1 as an optocoupler, this galvanic isolation circuit may also be made in the form of an isolation transformer, for example, a pulse transformer.
Generally, a galvanic isolation circuit is an expensive circuit and often impossible to integrate.